A known power seat apparatus is disclosed in JP2002-192996A (Reference 1). The power seat apparatus disclosed in Reference 1 includes a lower rail fixed to a vehicle floor, an upper rail supported by the lower rail so as to be slidable in a longitudinal direction of the vehicle and supporting a vehicle seat, and a screw shaft provided between the lower rail and the upper rail so as to extend in a direction where the upper rail is slidable. The power seat apparatus further includes a nut member fixed to the lower rail to engage with the screw shaft, a gearbox supported by the upper rail and connected to one end of the screw shaft, and a motor transmitting a drive force to the screw shaft via the gearbox. The screw shaft is driven to rotate by rotations of the motor to thereby slide the upper rail relative to the lower rail in the longitudinal direction of the vehicle.
According to Reference 1, as a security measure for a possible application of a large load to the vehicle seat, two washers and a collar are provided at the screw shaft in a manner that the collar is arranged between the two washers. Then, a recess, which is formed by making two cuts in a side face of the upper rail and bending a portion between the two cuts inward, faces a portion between the washers so as to be arranged between the two washers. As a result, the excessive load applied to the vehicle seat (specifically, the upper rail) is transmitted, through the recess that makes contact with either of the washers, to the lower rail to thereby endure the excessive load.
However, according to the Reference 1, the two washers and the collar are additionally provided, thereby increasing a cost and an assembly time.
A need thus exists for a power seat apparatus for a vehicle which is not susceptible to the drawback mentioned above.